Metal oxide thin film transistors (MOTFT) are gaining interest as high performance TFT backplanes for next generation display applications including active matrix liquid crystal displays, active matrix light emitting displays with organic light emitters (AM-OLED) or with inorganic crystalline light emitters (AM-LED). See for example the copending United States patent application entitled “Active Matrix Light Emitting Display” bearing Ser. No. 12/178,209, filed on 23 Jul. 2008, and incorporated herein by reference. Many of these large area applications use either glass or plastic substrates. To produce TFTs on large areas at low cost, it is advantageous to use low cost lithographic tools such as proximity/projection aligners rather than the more expensive stepper tools. Furthermore, due to deformation of substrates in processing (either glass due to high temperature treatment or plastic substrates due to chemical and heat treatment), the alignment issue has to be solved. Typically, misalignment due to deformation increases with the size of the exposure field. One way to compensate for the deformation is to reduce the exposure field by performing multiple exposures on the substrate and then stitching the multiple patterns together. However, this process substantially increases the manufacturing cost due to lower through put and the high cost of stitching.
It would be highly advantageous to have a self-aligned process in which there are no critical alignment steps.
Accordingly, it is an object of the present invention to provide new and improved methods of fabricating self-aligned metal oxide TFTs.
It is another object of the present invention to provide new and improved methods of fabricating metal oxide TFTs including no critical alignment tools or steps and using a minimum of process steps.
It is another object of the present invention to provide new and improved methods of fabricating metal oxide TFTs with metal source/drain contacts and buslines with improved thickness to wide ratio and with improved electric conductance.
It is another object of the present invention to provide new and improved methods of fabricating metal oxide TFTs with laser writing for patterning following layers after the 1st metal layer. (Use 1st photo mask to pattern critical structures as much as one can and self-align to fill in the rest.
It is also another object of the present invention to provide new and improved methods of fabricating metal oxide TFT arraies on a transparent substrate with low dimension stability in which only one high quality mask is used to define patterns on the first metal layer, and the critical patterns in the following layers are patterned by combinations of self-alignment with the first metal layer below, and additional patterning with low accuracy photolithography, laser writing or an add-on printing method.